<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <script src="https://cdn.jsdelivr.net/npm/vue@2.6.10/dist/vue.js"></script>
</head>

<body>
    <div id="app">
        <input type="text" v-model="msg" />
        <button @click="count++">累加count</button>
        doubleCount:{{doubleCount}}
    </div>
    <script>
        Vue.config.productionTip = false;

        const vm = new Vue({
            el: "#app",
            data() {
                return {
                    msg: "",
                    count: 2,
                }
            },
            computed: {
                doubleCount() {
                    return this.count * 2;
                }
            },
            /*

              wacth可以监听一个data属性或者一个计算属性
              就会触发watch侦听的回调函数
              我们可以在回调函数中做后续的事情
              
            */
            watch: {
                msg(newVal, oldVal) {
                    console.log("发送请求", newVal, oldVal);
                },
                doubleCount() {
                    console.log("重新计算了count");
                }
            }
        })
    </script>
</body>

</html>